The present invention generally relates to information recording and reproducing and, more specifically, to a recording and reproducing apparatus and a method for achieving high density recording of information transmitted at varying speeds.
The extensive research and development effort in the field of data recording and reproducing has resulted in many significant improvements in apparatus that record and reproduce information with respect to tape as well as other mediums. While there have been many different formats that have been developed for data recording and reproducing, the format wherein signals are recorded on magnetic tape as the tape is transported in a helix around a cylindrically-shaped tape guide drum has exhibited many distinct advantages in terms of relative simplicity of the tape transport drive and control mechanism, the necessary electronics involved, the number of transducing heads, and the efficient use of tape, in terms of the quantity of tape that is required for recording a given amount of material. By helically wrapping the tape around a tape guide as it is scanned by a rotating head, a single transducing head assembly can be utilized for reproducing or playing back the information that is recorded on the tape. When a single head assembly is used in a helical tape recording apparatus, two recognized alternatives are available for wrapping the tape about the tape guide for scanning by the rotating head, which are generally referred to as the "alpha" wrap and the "omega" wrap.
In apparatus employing the alpha wrap, the tape is introduced to the tape guide drum from one side and is helically wrapped completely around the drum so that it exits on the opposite side. It is referred to as the alpha wrap for the reason that the tape path about the tape guide drum generally conforms to the Greek symbol alpha (.alpha.) when one views the tape path from above. In apparatus employing the omega wrap, the tape introduced to the tape guide drum along a path that is generally radial relative to the tape guide drum, is passed around a guide post that directs the tape into contact with the surface of the drum, is helically wrapped around the drum or a portion thereof, and is passed around another guide post so that it exits the drum also in a direction generally radial relative to the drum. The tape path about the tape guide drum generally conforms to the shape of the Greek symbol omega (.OMEGA.) when it is viewed from above. Both of these wrap configurations are helical in that the tape is wrapped around the tape guide drum in a helical manner, with the tape exiting the tape path about the drum surface at a different axially displaced position relative to the position at which the tape enters the tape path. In other words, if the axis of the drum is vertically oriented, the tape leaves the drum surface at an axial position that is either higher or lower than the axial position at which it first contacts the surface. As the tape is passed around the tape guide drum, a rotating head assembly records data information signals along discrete parallel tracks that are oriented at an angle relative to the longitudinal direction of the tape so that a track length greatly in excess of the width of the tape can be achieved. The angular orientation of the recorded tracks is a function of both the speed of the tape being transported around the tape guide drum as well as the speed of rotation of the scanning head itself. The resultant angle therefore varies depending upon the relative speeds of both the rotating scanning head and tape being transported.
It should therefore be appreciated that if information signals are recorded on a tape at a predetermined angle which results from a precise rotational scanning head speed and tape transport speed, the subsequent reproducing of the information signal should be performed at the same speeds or the transducing head will not follow the track with precision. This assumes, however, that the head is rotating in the same equatorial plane. If the tape speed is changed during the reproduction of recorded information, such as reduced or stopped, the transducing head scans the tape at a different angle relative to the longitudinal direction of the tape, and therefore, will no longer precisely follow the recorded track and may even cross onto an adjacent track. The failure to precisely follow the track in registry during playback results in improper reproduction of the recorded information. While various prior art systems have been proposed to attempt to reduce such undesirable effects due to the lack of registry, many of such systems have not been entirely successful. Moreover, some prior art systems experience tracking difficulties during reproducing at the tape and head speeds that are intended to be identical to those that were used during recording.
One prior art system employs two transducing heads with switching means that are adapted to select the transducing head which has the maximum output. This approach suffers because neither head is always precisely on the recorded track throughout its length. As a result, the signal-to-noise ratio is poor. Other systems for reproduction of helically recorded signals have attempted to minimize the effect of mistracking by using synchronization pulse lineup techniques and the like, and by modifying the head-to-tape scan angle by changing the orientation of the axis of the tape guide drum about which the tape passes during recording and reproducing.
More recently, the above problems were overcome or substantially mitigated in a recording apparatus described in U.S. Pat. No. 4,165,523, entitled "Automatic Scan Tracking" by Richard A. Hathaway. Further description of this recording apparatus is set forth in U.S. Pat. No. 4,151,569, and U.S. Pat. No. 4,151,570. The apparatus described in these patents is directed to successfully achieving altered time base reference effects in the art of recording and reproducing information signals on a medium with a single transducing head. More particularly, such apparatus employs a cantilevered bimorph element anchored at one end and having the transducing head located on the second free end such that the head may be moved. This arrangement is satisfactory for single track recording and reproducing but cannot be moved sufficiently for a multiplicity of parallel tracks, such as, for example, 27 or more extremely narrow parallel tracks. An arrangement is therefore required that can move a multiple transducing head assembly a large distance, such as, for example, within the range of 0.02 to 0.04 inch. Moreover, if a multiplicity of transducing heads are employed in a single head assembly for recording and reproducing from a corresponding multiplicity of extremely narrow parallel tracks of data on a medium, accurate tracking becomes more critical and a different arrangement is preferred.